It is known that the physicochemical properties of solids in particulate form are influenced by the size and shape of the particles. As particle size diminishes in scale, there is an enhancement of properties, and often the inception of new properties.
New commercial products are becoming available which provide special advantages because of fine particle size. Alkali metal bicarbonate, in particular, is a common reagent which has found application in a broad variety of products such as health care products, skin cleansers, skin care products, dentifrices, toothpolish, soft scrub cleansers, hard surface cleansers, agricultural products and the like.
There is evidence that fine particle size alkali metal bicarbonate can exhibit increased reactivity in comparison with coarse grain alkali metal bicarbonate. For example, in soda cracker production, finely divided sodium bicarbonate ingredient is more efficiently distributed and effectively reactive during the cracker dough preparation. The finished baked cracker is an improved product which has a substantially uniform texture, flavor and surface color, and a consistent pH throughout.
The coarse grain alkali metal bicarbonate particles of the prior art are often combined with liquid mediums to form slurrys. These prior art slurrys, however, are unstable and result in the formation of distinct layers of alkali metal bicarbonate particles and liquid medium after only a few minutes. These prior art slurrys, therefore, require the presence of a suspending aid which promotes stability in the otherwise unstable slurrys. The presence of a suspending aid, however, increases the cost of producing such slurrys. In addition, the presence of the suspending aid increases the likelihood of interaction between the components of the slurrys. In other utilities, the presence of a suspending aid is detrimental or prohibited by the end use of the product.
The solubility of prior art alkali metal bicarbonate particles falls off as temperature decreases. An alkali metal bicarbonate slurry, when combined with additional water to form a dilution, demonstrates decreased solubility of the alkali metal bicarbonate particles. This decreased solubility is apparent particularly at temperatures below 25° C. For example, a dilution made from a sodium bicarbonate slurry (the slurry being about 70% by weight of sodium bicarbonate particles, based upon 100% total weight of the slurry) and additional water at 22° C. will have 8.5% alkali metal bicarbonate particles dissolved therein. However, at 10° C., the dilution decreases to 7% alkali metal bicarbonate particles. Thus, time and fuel must be used to increase the temperature in order to facilitate the dissolution of the sodium bicarbonate particles. When such dilutions are used as dialyzates, both the cost and time of the medical treatment is increased.
Thus, there is continuing interest in the development of micron and submicron sized alkali metal bicarbonate particles, and slurrys containing the same, which exhibit a novel combination of properties, including increased stability and solubility, when utilized in health related, personal care, biologically active, household, and specialty type products.
Accordingly, it is an object of this invention to provide particulate alkali metal bicarbonate having a median particle size of from about 0.2 to about 50.0 μm with the particles having a surface area of from about 120 to about 140 cm3 μg. The preferred range is from about 127 to about 130 cm3/g.
It is another object of this invention to provide a stable, flowable slurry comprising alkali metal bicarbonate particles dispersed in a liquid medium, the particles remaining in suspension for an extended period of time without the requirement of a suspending aid.
It is another object of this invention to provide a stable, flowable slurry comprising alkali metal bicarbonate particles dispersed in a liquid medium, the particles having a median particle size of from about 0.2 to about 50.0 μm and a surface area of about 120 to about 140 cm3/g. The slurry has a Zeta potential of from about 2 to about 11 mV and loose bulk density of about 1.40 to about 1.60 g/mL, and preferably about 1.49 g/mL.
It is another object of this invention to provide a stable, flowable slurry where the alkali metal bicarbonate particles are sodium bicarbonate particles having the particle size, surface area, Zeta potential and loose bulk density described above, as well as an IR spectra in the range of from about 4,000 cm−1 to about 400 cm−1, and preferably as shown in FIG. 1.
It is another object of this invention to provide an aqueous dilution containing alkali metal bicarbonate particles which may be prepared at a relatively low temperature and achieve a saturated solution in excess of non-invention materials.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.
Publications of background interest with respect to the present invention subject matter include U.S. Pat. Nos. 5,411,750, 5,424,077, 5,466,470, 5,518,727 and 5,645,840, incorporated herein by reference in their entirety.